Progressive dry kiln and method of drying lumber



J. B. WELCH 1,753,974

PROGRESS IVF DRY KILN AND METHOD OF DRYING LUMBER April 8, 1930.

SSheets-Sheet l .Eiled Oct. so, 1925 all/y.

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J. B. WELCH 1,753,974

I PROGRESSIVE DRY KILN AND METHOD OF DRYING LUMBER April 8, 1930.

5 Sheets-Sheet 2 Filed Oct. 30, 1925 tier. Ma MM,

A O I PROGRESSIVE DRY KILN AND METHOD OF DRYING LUMBER J. B. WELCH Filed Oct. 30, 1925 s Sheets-Sheet Patented Apr. 8, 193% i UNITED STATES JOHN B. WELCH, OF NEW ORLEANS, LOUISIANA PROGRESSIVE DRY KILN AND METHOD OF DRYING LUMBER Application filer [October so, 1925. Serial No. 65,763.

This invention relates to a progressive dry kiln for drying lumber and also to a method of drying lumber.

, One object of the invention is to provide a novel and improved construction of progres sive dry kiln in which the air and drying conditions within'thekiln may be controlled and regulated in a novel and highly eflicient manner. v

A further object of the invention is-to provide a novel and improved construction of progressive dry kiln which is particularly adapted forause in drying hardwood, and in which provision is made for maintaining the '15 requisite temperature conditions within the kiln and at the same time an eflicient recirculation of the air to produce most advantageous drying results.

A still further object of the invention is to as provide a novel and improved method of dryuse indrying hardwood. With these objects in view, the invention ing lumber which is particularly adapted for consists in the apparatusv and in the method hereinafter described and particularly defined in the claims at the end of this specification. 1 V

In the drawings, Figures 1 and 2 illustrate in vertical longitudinal section, a progressive dry kiln embodying the present invention; Figs. .3 and 4c are views in horizontal section taken upon two different planes, located so as to show one of the air ducts in plan and the other in longitudinal section, and Figs. 5 and 6 are horizontal longitudinal sections taken above the heating coils with the upper lower tier of heating coils broken away to illustrate the lower tier of heating coils, at the right-handend of the apparatus.

In drying lumber and other material, the more modern practice contemplates the initial heating of the green materialthroughout in an atmosphere of sufficiently highly humidity to accomplish the heating without evaporation of appreciable moisture from the green material. After the material has thus been heated thoroughly to a sufficiently high temperature, the material is brought into contact with air of gradually decreasing humidity,

thereby permitting gradual evaporation of the moisture and preventing surface drying,

cracking and other disadvantagesu In drying lumber on a large scale progressive kilns are usually employed which comprise elon-j gated chambers often of a-length'approximating 100 to 200 feet. During the operation of the kiln, the lumber is progressively moved from the entrance or wet end of the kiln to the dry or delivery end of the kiln.

Provision is made for maintaining the temso;

perature and humidity conditions within the kiln such that the entering or green lumber is initially brought into contact with air of relatively .high humidity, such that premature evaporation of the moisture within and 55.

throughout the body of the lumber is prevented. After the lumber has become thoroughly heated, it is progressively moved to the dry or delivery end of the kiln, and in the course of its movement, encounters air of progres sively decreasing humidity, so thatthe moisture is caused to gradually evaporate in a manner such as to' avoid surface drying, cracking and similar difliculties.

.In drying hardwood it is essential to maintain a definite and considerable difference in temperature of the air at the green and the dry ends of the kiln, and in order to produce most efl ectivedrying, it is desirable that an efficient recirculation of the air should be provided within the kiln. In accordance with the present invention provision is made for maintaining the requisite recirculation of air within the kiln without interfering with the maintenance of the desired temperature differences between the green and the dry ends of the kiln. In accordance with the preferred method and in the preferred form of apparatus, thisis accomplished by heating difierent sections of the 'kiln to different temperatures, progressively increasing from the green to the dry end of the kiln, and'also by recirculating the. air within the kiln in a plurality of paths, which preferably extend from the several sections of the kiln to the dry end thereof.

Referring to the drawing, 10 represents the elongated drying chamber through which the lumber to be dried is passed. The chamber is provided with the usual openings-12, H at the opposite ends thereof through which the lumber is introduced into and delivered from the kiln. Suitable doors (not shown) are provided for normally closing such openings, the construction and operation of which may be as usual in progressive kilns. The lumber during its movement through the kiln is sup ported upon the usual tracks 20 and the requisite amount of humidity is introduced into the kiln by admitting live steam from the several steam nozzles 24 exactly as is standard practice in progressive dry kilns at the present time.

In accordance with the present invention, recirculation of the air within the kiln is caused to take place in a plurality of paths, and also the heating coils indicated by the general reference 30 are so arranged as to divide the kiln into a plurality of sections heated to different temperatures, and which sections are herein shown as three in number, although if found desirable more or less may be used. The section A at the green or entrance end of the kiln is heated by two sets of steam coils 31, 32-, arranged to extend along the sides of the kiln and to provide a free space between them offering no obstruction to the rapid downward movement of the air through the lumber at this section of the kiln. The heating coils 31, 32 are fed from a source of steam supply (not shown) through a feed line 47 and the steam supply to each is controlled by a suitable valve 53. The second section B of the kiln is provided with additional steam coils 33, 34, which supplement the heating power of the coils 31, 32 to increase the temperature range in the section B. The opening or space between the coils 33, 34 is more restricted than the space at the section A. The section C comprising the dry end of the kiln is provided with a third set of heating coils 35, 36 adapted to supply the heat necessary to perform the final drying upon the lumber, and which supplement the heating coils 31, 32, and 33, 34, to enable the temperature of the section C to be maintained at a relatively high point. The coils 33, 34, and the coils 35, 36, are fed from a suitable source of supply, and the flow of the steam controlled by valves 55, 57 In Fig. 5 the upper banks of the coils 31 through 36 are broken off to show the lower banks of such coils. It will therefore be apparent that the arrangement of heating coils just described produces a heating of the air within the kiln which progressively varies in intensity at the different sections A, B and C, from the green to the dry end of the kiln, and that the lumber during its movement through the kiln is caused to pass through difierent sections of the kiln of increased intensity of heat.

In order to recirculate the air within the kiln without disturbing to any appreciable extentthe maintenance of the temperature conditions in the sections A, B and C, the

kiln is provided with one or more maln air ducts or conduits 40 located beneath the normal position of the lumber upon the rails 20 and which are herein shown as formed upon the bottom of the kiln below the tracks 20. Each main air duct 40 is provided with a plurality of suction openings 42, 43, 44, preferably one for each section A, B and C, and through which air is caused to pass downwardly from the different sections of the kiln and is delivered through the duct to be discharged under the lumber at the dry end of the kiln through suitable discharge openings or passages 45,-preferably comprising slots in the top of the duct. The recirculation of the air may be induced by the difference in densities of the air at the different sections of the kiln and also suitable steam aspirators 58 are preferably provided within the duct although other means of increasing the rate of air movement through the duct may be used. The steam aspirators 58 are preferably provided with suitable valves 59, one at each section, which afiord a means of selectively controlling the rate of recirculation of the air through each of the suction openings 42, 43, 44. Each duct 40 is also provided with a fresh air inlet 50,'so that the fresh air passing along through the duct mixes with the air withdrawn through the several openings 42, 43, 44, from the diiferent sections A, B and C of the kiln, and the air is thus caused to pass along through the duct 40 to be delivered at the .dry end of the kiln through the discharge slots 45, directly under the lumber. The air then rises and recirculates in several paths indicated by the arrows in Fig. 1.

From the description thus far, it will be observed that in the illustrated progressive dry kiln, the air within the kiln is moved in a plurality of paths toward the dry end of the kiln from a plurality of different sections of the kiln, thereby setting up recirculation in a plurality of different closed paths, and as a result it is possible by regulating the intensity of the aspiration at the different sections to recirculate the air and at the same time to prevent the green end of the kiln being heated up beyond its proper temperature by excessive recirculation of air from the hot dry end of the kiln. In other words only a minor proportion of the heat at the dry end of the kiln is circulated entirely back to the green end, so that when desired a definite temperature difference may be maintained between the green and dry ends of the kiln. In this manner it is possible to maintain those temperature conditions within the kiln most conducive to efficient drying of diiferent kinds of lumber, particularly of hard lumher. It will also be observed that in the pres ent kiln there is little chance of pockets of stagnant air remaining in the lower layers of the lumber as the air is recirculated down through the lumber at a plurality of points along the length of the kiln. The provision of a plurality of the aspirators and suction openings affords the operator flexible control 5 of conditions to suit the needs of the lumber as it is being moved through the kiln, so that in the event that different speciesof lumber are introduced into the kiln, conditions may be conveniently altered to provide the most efficient drying conditions for the particular lumber at any point during its movement through the kiln.

It will also be observed that the arrangement of the heating coils is such as to enable not only the desired graduated heating effect to be obtained from the green to the dry end of the kiln, but also at the green end and in the mid-section of the kiln, the centralportion of the kiln is left free from the heating coils providing a free passage for the air down through the lumber at these sections of the kiln.

While the preferred form of the invention has been illustrated and described, it is to be understood that the different features of the invention may be embodied in other forms within the scope of the following claims.

Having thus described the invention, What is claimed is 1. In a progressive dry kiln, an elongated heating chamber, heating coils arranged to provide different longitudinally spaced intensities of heat in different sections of the kiln, progressively increasing in intensity from the green to the dry end thereof, and means for causing recirculation of the air in the kiln in different paths from the different sections to the dry end of the kiln.

2. Apparatus of the character described comprising an elongated chamber, means for heating different longitudinally spaced sections of the kiln to different degrees of temperature, and means for producing recirculation of the air in a plurality of closed paths within the kiln, downwardly through the lumber at a section of lesser heat, and upwardly through the lumber at a section of higher heat.

3. In a drying apparatus of the character described, in combination, an elongated chamber, means for producing difi'erent intensities of heat in different longitudinally spaced sections of the chamber comprising a plurality of sets of steam coils arranged to provide unobstructed passage for the recirculation of the air downwardly through the lumber at the green end of the kiln and means for causing longitudinal recirculation of the air within the kiln in a plurality of different closed paths.

4:. In a drying apparatus of the character described, in combination, an elongated chamber, means for producing difierent intensities of heat in different sections of the 3 chamber comprising a plurality of sets of steam coils arranged to provide unobstructed passage for the recirculation of the air downwardly through the lumber at the green end of the kiln and through the center of the lumber in the middle section of the kiln.

5. In a drying apparatus of the character described, in combination, an elongated chamber, means for producing different intensities of heat in different sections of the chamber, and means for recirculating the air including a main air duct provided with a plurality of suction openings located at different stations along the length of the chamber, and supplemental means for producing air-movement through the duct.

6. In a drying apparatus of the character described, an elongated chamber, means for recirculating air within the chamber, including an air duct provided with a plurality of suction openings spaced at different points along the length thereof.

7. In a drying apparatus of the character described, an elongated chamber, a'main air duct provided with a plurality of suction openings therein communicating with the interior of the chamber at different points along the length thereof, and supplementalmeans near said suction openings for adjust-ably controlling the rate of air drawn through said suction openings.

8. In a drying apparatus of the character described, in combination, an elongated chamber, and means for moving air toward the dry end thereof from a plurality of different longitudinally spaced sections of the chamber.

9. In a drying apparatus of the character described, in combination, a drying chamber, heating devices arranged to provide different longitudinally spaced intensities of heat in the difierent sections of the drying chamber, and means for recirculating'the air within the chamber, including means for conducting air from a plurality of the sections in a plurality of difierent paths to a different point in the drying chamber.

In testimony whereof I have signed my name to this specification.

JOHN B. WELCH. 

